1. Field of the Invention
This invention relates to telescopic scopes used with firearms and, more particularly, to scopes that can be xe2x80x9czeroed-inxe2x80x9d for more accurate long range shooting.
2. Description of the Related Art
Riflescopes, telescopic scopes for rifles, are commonly used by hunters to aim their rifles at selected targets. During use, the hunter looks into the scope and positions the target within the field of view of the scope reticle. Because gravity causes the bullets to drop when they exit the rifle barrel, the angular position of the scope with respect to the rifle barrel must be compensated so that the impact point of the bullet matches the target seen on the scope reticle. The act of adjusting the angular position of the scope with respect to the rifle barrel is known as xe2x80x9czeroing-inxe2x80x9d.
Typically, a scope is zeroed-in by the hunter when firing bullets at a target at a known distance. After viewing a group of impacts on the target, the hunter determines the distance of drop and then adjusts the angular position of the scope with respect to the rifle barrel. The hunter continues to use this xe2x80x9ctrial by errorxe2x80x9d method until the scope proper position, known as the xe2x80x9czero pointxe2x80x9d, is determined.
Many scopes include adjustment knobs that enable the hunter to easily xe2x80x9czero-inxe2x80x9d0 the scope and adjust the angular position of the scope for targets at distances greater than the distance used to xe2x80x9czero-inxe2x80x9d the scope. For example, if the scope is xe2x80x9czeroed-inxe2x80x9d at 200 yards, the adjustment knob may be used to adjust the angular position of the scope so that the reticle accurately views the more distant impact point (i.e. target). If the target moves towards or away from the user (i.e. 250 yards), the hunter must quickly readjust the adjustment knob so that the scope is positioned correctly.
In order to quickly readjust the angular position of the scope, the hunter must remember the adjustment knob current setting, the direction of rotation to increase or decrease the angle, and the number of xe2x80x9cclicksxe2x80x9d, or rotations of the knob, needed for the new setting. If the clicks are difficult to hear or feel or if the environment is dark, accurate adjustments can be difficult or impossible to make.
In order to prevent confusion, most scope manufacturers limit the movement of the adjustment knob to less than two rotations. Also, most scope manufacturers calibrate the adjustment knobs so that there are 60 to 120 clicks in one rotation and one click is equal to 1 inch to xc2xd inch adjustment in elevation of the target at 100 yards. Using this calibration standard, a typical scope maximum range of adjustment at 100 yards is 60 inches. When the above method is used to xe2x80x9czero-inxe2x80x9d the scope, a substantial amount of rotation may have been used. Thus, the total number of clicks available for adjusting the position of the scope is reduced which seriously limits the usefulness of the rifle for shooting at long-range targets. Another drawback with using a relatively large calibration such as a xe2x80x9c1 click equals 1 inch standardxe2x80x9d is that it introduces a greater error at greater ranges. For example, if a target is located at 300 yards, an error of one click represents 3 inches in elevation.
What is needed is a scope elevation adjustment mechanism that enables the user to easily xe2x80x9czero-inxe2x80x9d the scope at any position and still allow for full and unlimited rotation of the adjustment knob, and that also allows the adjustment knob to be used for finer adjustments.
It is an object of the present invention to provide a riflescope with an adjustment knob for changing the angular position of the rector tube.
It is another object of the present invention to provide such a riflescope that enables the user to set the xe2x80x9czero-inxe2x80x9d point on the riflescope at any point of the riflescope range and still use the full range of adjustment of the adjustment knob.
It is a further object of the present invention to provide such a riflescope that uses xe2x80x9c{fraction (1/4)} minute per clickxe2x80x9d fine adjustment setting for greater accuracy.
These and other objects are met by a zero stop riflescope adjustment mechanism that allows a user to establish the xe2x80x9czero pointxe2x80x9d at any point in the range of the scope, and still maintain xc2xc minute clicks and unlimited rotations of the adjustment knob. The mechanism includes an adjustment bolt longitudinally aligned inside a cylindrical-shaped adjustment body that fits into a standard threaded hole formed on the turret of the riflescope. The adjustment bolt is a T-shaped structure with upper and lower threaded sections and a wide, central circular collar. During assembly, the lower threaded section of the adjustment bolt is connected to a lower threaded bore formed inside the adjustment body. The lower neck of the adjustment body connects to the threaded bore while the lower end extends into the hole formed on the turret and contacts the rector tube. When the adjustment bolt is rotated inside the adjustment body threaded bore, the distal end of the adjustment bolt advances or withdraws from the hole in the turret to change the angular position of the rector tube inside the riflescope.
When the adjustment bolt is properly connected to the adjustment body, the upper section of the adjustment bolt extends above the top surface of the adjustment body. Disposed longitudinally over the adjustment body is an index dial with a central bore formed therein that receives the threaded upper section of the adjustment bolt that extends above the adjustment body. The index dial includes a top surface with a central bore formed therein and a vertically aligned index line formed on its outside surface. During assembly, after the adjustment body is tightened and securely attached to the turret, the index dial is aligned over the adjustment body so that the threaded upper section extends through the index dial and the index line faces the shooter. An upward extending tab element is formed on the top surface of the index dial which acts as a stop surface for a downward extending tongue member on the bottom surface of the stop ring. After the adjustment body is tightened and securely attached to the turret, the index dial is aligned over the adjustment body and locked in position so that the index line faces the shooter.
Threadingly attached to the threaded upper section of the adjustment bolt that extends above the index dial is a stop ring. Attached to the outer perimeter of the stop ring is a downward extending tongue member that contacts the upward extending tab element formed on the index dial when the stop ring is rotated downward and positioned against the index dial. Together, the tab element and tongue member act as a stop means to prevent downward advancement of the stop ring over the adjustment bolt.
Threadingly attached to the threaded upper section on the adjustment bolt and above the stop ring is a lock ring. During use, the lock ring is rotated downwardly over the threaded upper section until it is pressed tightly against the top surface of the stop ring. Connecting means, such as screws, are then used to connect the lock ring and stop ring together which pinches them against the threads on the adjustment bolt thereby securely locking the lock ring and stop ring in a fixed position on the adjustment bolt. When the lock ring is rotated, the adjustment bolt is rotated inside the adjustment body until further downward rotation of the adjustment bolt is prevented by the index dial containing the stop ring.
A cylindrical-shaped outer cap is then longitudinally aligned and inserted over the threaded upper section of the adjustment bolt, the lock and stop rings, the index dial, and the adjustment body. A locking screw is then used to lock the outer cap to the lock ring.
Formed inside the upward extending cavity inside the adjustment body is a plurality of longitudinally aligned splines. As mentioned above, the adjustment bolt is initially attached to the threaded bore formed in the adjustment body. When properly connected thereto, the outer surface of the bolt circular collar extends outward and is disposed adjacent to the splines formed on the adjustment body. Disposed on the outer surface of the circular collar is a transversely aligned ball screw which extends outward and contacts one of the splines. When the adjustment bolt is rotated, the ball screw travels over the splines thereby providing a rotational, resistant force and making a characteristic xe2x80x9cclickingxe2x80x9d sound. The ball screw may include an optional tension adjustment means that enables the user to set the outward force exerted by the ball screw over the splines thereby enabling the user to adjust the amount of torque required to turn the adjustment bolt.